This invention relates to a brake assembly and is more particularly concerned with a brake assembly of the constant friction type where a sufficient level of braking torque is required to be applied to a rotary drive shaft in at least one direction of rotation thereof.
Constant friction brake assemblies are used on rotary drive shafts for controlling aircraft wing flaps. Typically, when the flap is being extended, the load applied to the flaps by the airflow passing over them acts in the opposing direction to the force being applied by the operating shaft. Under this condition, it is necessary to reduce friction provided by the brake. When the flap is being retracted, the load applied to the flap by the airflow assists in the retraction and so, in this direction of rotation of the drive shaft, the brake assembly acts to provide a greater braking effect. It is common with this type of system to provide a brake assembly where the brake automatically operates on failure. This has the advantage that, when a failure occurs, e.g. a shaft breakage, the friction brake should be able to hold the load assuming that the load tends to blow the flaps up, i.e. in the retracting direction. The benefit of this type of constant friction brake is that it acts automatically, i.e. does not require to be signalled to operate.
There is a need to check for dormant faults in the brake assembly, and this is currently done by a physical check only at pre-determined periods; dormant faults may thus exist between checks and the detection of failure is dependent on the correct scheduling of maintenance.
It is an object of the present invention to provide an improved brake assembly which can enable rapid and reliable identification of a braking fault.
According to the present invention, there is provided a brake assembly comprising a rotary member; a constant friction brake device acting on the rotary member to apply a braking torque to the rotary member in at least one direction of rotary movement of the latter; and signalling means for signalling when a predetermined braking torque has been exceeded.
Thus, the present invention can enable a positive signal to be given each time the brake device has operated satisfactorily. Accordingly, failure of the signalling means to signal indicates the need to inspect for a potential failure of the brake assembly.
In a preferred embodiment, the constant friction brake device comprises:
at least one first friction element mounted for rotary movement with the
rotary member,
a fixed member,
a friction element support mounted for rotation relative to the fixed member,
at least one second friction element mounted on the friction element support so as to be frictionally engageable with said at least one first friction element in at least one direction of rotary movement of the rotary member; and
a detent mechanism acting between the fixed member and the friction element support, said detent mechanism being adapted to retain the friction element support against rotation below said predetermined braking torque;
and wherein the signalling means is arranged to signal when the detent mechanism has operated to permit relative rotation between the friction element support and the fixed member.
The detent mechanism may be a resilient latch mechanism (e.g. a ball and recess mechanism) such that disengagement of the latch permits rotation of the friction element support relative to fixed member. Alternatively, a pre-loaded spring or other pre-loaded compliant member may be used.
The signalling means may include a proximity switch which is arranged to be actuated when the friction element support moves relative to the fixed member. Instead of using a proximity switch, a microswitch or other type of relative movement sensor may be employed, e.g. a linear variable differential transducer.